SEISMIC RELIABILITY-BASED DESIGN OF STRUCTURES ISOLATED BY FPS

The paper deals with the seismic reliability of base-isolated structural systems equipped with friction pendulum isolators (FPS) in order to provide useful design recommendations. A two-degree-of-freedom model is adopted by accounting for the superstructure flexibility, whereas the FPS isolator behaviour is described by adopting a widespread model which considers the variation of the friction coefficient with the velocity. The spectral displacement corresponding to the isolated period has been chosen as intensity measure (IM). The uncertainty in the seismic inputs as well as the friction coefficient at large velocity are considered as random variables modeled through appropriate probability density functions. Monte Carlo simulations are developed in order to evaluate the probabilities exceeding different limit states related to both superstructure and isolation level defining the seismic fragility curves. Finally, considering the seismic hazard curve related to an Italian site, closedform expressions are derived with the aim to design the radius in plan of the friction pendulum isolators in function of the expected reliability level.